1. FIELD OF THE INVENTION
This invention relates to a method of treating waste sludge to remove the heavy metal contaminants therefrom, and the utilization of the resultant product of the removal process in the manufacture of building products such as brick, cinder blocks, concrete aggregate and other construction materials.
2. ART BACKGROUND
Currently available methods for purifying water and industrial sludge are generally incapable of removing certain chemicals and biologically active substances that are appearing in water supplies in increasing proportions. The continued pollution of our water is becoming more alarming as the mechanisms for purifying the water are shown to be unable to handle the large and increasing supply and variety of contaminants.
Standard methods for purifying water include coagulation, sedimentation, filtration and chemical treatment. Such methods are effective for removing most contaminants and for killing most of the microorganisms present. These methods, however, are not completely effective for removing substances such as hormones, pesticides, viruses, toxins and, most importantly, for the present purposes, heavy metal cations.
The waste of many high tech industries is particularly problematic because heavy metals, which are used in many of the manufacturing processes in the plating, semiconductor and computer industries, are toxic to living organisms.
A large number of prior art processes are available for the extraction of toxic waste from water and industrial sludge. Many of these processes utilize various types of clay, either natural or partially synthesized, to absorb or adsorb the heavy metals and other toxic materials such as viruses, hormones, pesticides, bacterial toxins and the like from water and industrial waste.
Sawyer, U.S. Pat. No. 4,054,515 discloses a method of treating water with various grades of specified clays, including attapulgite and sepiolite, by contacting the water with such clays or percolating the same through the clays. However, the Sawyer clays are formed in accicular-type needles disposed in solution in order to extract the heavy metal cations and other contaminants. Other relevant patents relating to the processing of industrial sludge and water waste include U.S. Pat. Nos. 4,676,907; 4,067,894; 4,116,828 and 4,517,095.
One problem which has evolved with these processes is that the material used to purify the water is then, itself contaminated and must be properly treated and disposed of. In the past, this type of processing of the purification material included loading the same into metal containers and disposal thereof in landfills and underground containment systems, and in some cases, the disposal of the purification material without packaging into landfills and the like. This means of disposal is particularly wasteful in that it requires a substantial amount of manpower to carefully handle the purification materials, process the purification materials and dispose of them in an appropriate manner. More costs are obviously involved in the landfills and underground storage of such materials. A substantial drawback to the above-described prior art is that the long term storage of these waste processing materials is generally wasteful in that they are merely disposed of in storage dumps with possible long term environmentally deleterious effects and resulting on-going liability, and there is no useful purpose for the waste materials as well. Estimates are that it costs approximately $400-$1,200 per ton to process hazardous waste, ship and dispose of the same at legal dump sites.It would be desirable to provide a process which would eliminate long term storage risks and substantially reduce the cost of disposing of the heavy metal waste contaminants by converting them to safe useful products.
There have been recent reports relating to a processing plant in San Diego whereby heavy metals and other contaminants were removed from municipal waste sludge and converted to ceramic pellets which could be mixed into concrete. This concrete material is alleged to be safe and further, provides a useful outlet for disposing of the various toxic wastes having to utilize landfill sites.